1. Field of the Invention
The present invention relates to lifting cranes and more particularly to lifting cranes for use on jack-up type drilling rigs and lift boats and the like wherein the rig includes a barge that can be lifted above the water's surface on legs and wherein the crane fits on the deck of the barge about the leg, but spaced from the leg and its adjacent jacking structure. Even more particularly, the present invention relates to an improved jack-up rig crane that utilizes a support ring beam having an L-shaped cross-section that is mounted structurally to the barge about the leg elevating units but spaced therefrom so that the ring beam develops all structural load of the crane gantry, boom and live load through the barge deck. A crane gantry mounts upon the ring but about the leg and jacking structure. Roller bearings engage the front and rear portion of the gantry for transferring load to the ring. A lift boat is a self-propelled, self elevating vessels generally with a clear deck, personnel quarters, and a lifting crane.
2. General Background
Lift boats are well known in the art. These devices include a floating hull that allows the boat to be transferred from one marine location to another. When the hull reaches a desired location, such as a proposed oil well, typically three or four legs are lowered from the barge to the sea bed. These legs are then powered downwardly to lift the hull vertically on the legs and above the water's surface.
Once in operating position, a jack-up rig presents a stable platform surface for oil and gas well drilling operations, work over operations, repair work etc., notwithstanding the wave action at the water surface below.
There have been many patents that have issued relating to jack-up rigs. An example of a recent patent that covers a jack-up rig is U.S. Pat. No. 5,139,366 issued to Kenneth Choate and John Laird entitled "OFFSHORE JACK-UP RIG LOCKING APPARATUS AND METHOD". The Choate patent provides a locking apparatus and method for an offshore jack-up rig having at least one leg extending through the hull and at least one set of rack teeth attached to each of the legs. One or more locking bars are supported from the hull and are movable in a direction substantially normal to the face of the rack teeth. A piston and cylinder power assembly moves the bars towards the teeth and a retention system engages the bars holding them in engagement with the teeth. The elevating system of the rig co-acts with the set bars to lock the hull and legs together.
Another recent patent that relates to jack-up rigs and explains there operation is U.S. Pat. No. 4,813,814 entitled "LEG-HOLDING DEVICE FOR OFFSHORE PLATFORM".
Other examples of patents that have issued and relate generally to jack-up rigs include the LeTourneau U.S. Pat. No. 4,722,640; Thomas U.S. Pat. No. 4,627,768; the Hotta U.S. Pat. No. 4,589,799; the Grzelks U.S. Pat. No. 4,505,616; and the Colin U.S. Pat. No. 4,482,272.
A patent that illustrates the elevating and lowering of a jack-up rig in a marine environment is the Thomas patent (see FIGS. 4a-4f) U.S. Pat. No. 5,224,798, entitled "OVERLOADING DEVICE FOR A JACK-UP OIL PLATFORM AND PLATFORM INCLUDING THE DEVICE".
Each of these jack-up type platforms presents a unique problem for the user, namely that of lack of space. Jack-up rigs are normally used in oil and gas well drilling. The deck of such vessels is thus required to carry a derrick for oil and gas well drilling operations, racks of drill pipe for use in the oil and gas well drilling operations, drilling mud and related chemicals that are used in the drilling operation as well as pumps, motors, fuel supply and the like. In short, space is in high demand on a jack-up rigs.
One of the essential elements of a lift boat is a lifting crane that can be used to lift supplies from its own deck, work boat, supply boat or the like, and place those supplies on the platform. Some years ago, a patented crane apparatus was designed to fit over the leg of a smaller sized lift boat wherein the leg was of a cylindrical pipe configuration. The Gordon U.S. Pat. No. 4,417,664 disclosed generally the concept of mounting a crane having a gantry and a boom about the leg of a lift boat.
Another patent that addressed the problem of mounting a crane on a jack-up rig (lift boat) where there is limited space is the Gunther, Jr. et al. U.S. Pat. No. 4,652,177. This patent proposes to mount the crane on the jacking structure or jacking tower of the jack-up rig (lift boat). However, such an arrangement presents a support for only very lightweight cranes and does not address the problem of mounting a very substantial crane on a much larger jack-up rig wherein the legs each have a truss-like triangular configuration or large cylindrical legs. It is to this problem that the present invention is directed.